/**
 * Definition for singly-linked list.
 * class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    class ListNode {
      int val;
     ListNode next;
      ListNode(int x) {
          val = x;
          next = null;
      }
  }
    public boolean hasCycle(ListNode head) {
        if(head == null){
            return false;
        }

        ListNode slow = head;
        ListNode fast = head;
        while(fast!=null && fast.next != null){
            fast = fast.next.next;
            slow = slow.next;
            if(fast == slow){
                return true;
            }

        }
        return false;

    }
}